LINES
AND
WAVES
Faraday, Maxwell
And 150 Years
Of Electromagnetism
Robert D. Friedel
Center for the History of Electrical Engineering
Institute of Electrical and Electronics Engineers
This publication was prepared in conjunction with a
traveling exhibit created by the IEEE Center for the
History of Electrical Engineering in commemoration of
the 150th anniversary of the birth of James Clerk Maxwell and of Michael Faraday's discovery of electromagnetic induction. Funded by the IEEE and a number of its
constituent technical societies, the exhibit was circulated
by the Association of Science-Technology Centers to
museums in the United States and Canada.
Exhibit design and fabrication: HJB Associates, Alexandria, Virginia.
Publication design: Stephen Goldberg, IEEE Spectrum
Graphics supervision: Janet Mannheimer, Manager
Art & Production, IEEE Spectrum
Composition: Randi Applebaum, IEEE Spectrum
Copyright @ 1981 by the Institute of Electrical and Electronics Engineers, Inc. New York, New York.
Acknowledgements
Lines and Waves is a Centennial project of the Institute of
Electrical and Electronics Engineers (IEEE), and has been
created by the Center for the History of Electrical
Engineering. This exhibit has been made possible only by
the assistance of a number of institutions and individuals.
We gratefully acknowledge their help:
Division of Electricity, National Museum of American
History, Smithsonian Institution, Washington.
Burndy Library, Norwalk, Connecticut.
AlP Niels Bohr Library, New York.
The Royal Institution, London.
Cavendish Laboratory, Cambridge.
Engineering Societies library, New York.
The Institution of Electrical Engineers, London.
New York Public library.
Smithsonian Institution libraries, Special Collections
Branch.
National Aeronautics and Space Administration.
Special personal thanks to Prof. C.W.F. Everitt of Stanford University.
Library of Congress Catalog Card Number: 81-7150
LINES AND WAVES
FARADAY, MAXWELL AND 150
YEARS OF ELECTROMAGNETISM
It was 150 years ago that the English scientist
Michael Faraday discovered that he could generate
electricity with magnets - the phenomenon we call
electromagnetic induction. In the same year that
Faraday made this discovery, there was born in
Scotland the man whose brilliant mathematical
interpretation of Faraday's ideas was to become the
foundation of our modern concepts of electricity,
magnetism and light, James Clerk Maxwell. This
exhibit celebrates the life and work of these two men
and seeks to highlight their contributions to our
understanding of electricity and our ability to make
electricity work for us through engineering.
This exhibit is sponsored by the Institute of
Electrical and Electronics Engineers and has been
produced by the IEEE's History Center. It is hoped
that exhibits such as this one will foster among both
electrical engineers and the general public an
appreciation for the diversity an richness of the
heritage of electrical engineering.
BEGINNINGS
Smithsonian Institution Libraries, Special Collections Branch.
Education
London, about the time of Faraday’s birth, New York Public Library
____________
Origins
Michael Faraday was born on the 22nd of
September, 1791 in the small town of
Newington, Surrey, near London. He was the
son of a poor blacksmith who was able to
provide his family with only the most
rudimentary schooling, supplied by the local
common day-school. Faraday's most important
legacy from his parents was his deep religious
faith. Born and raised a member of the small
dissenting sect known as the "Sandemanians,"
Faraday never lost, in a long life devoted to
science, his strong attachment to his church.
Faraday's formal schooling ended when he
was 13. Family circumstances required that he
then become an apprentice, both to support
himself and to learn a useful trade. It was
remarkable good fortune that he was sent to
the shop of Mr. G. Ribeau, a bookseller and
bookbinder, for there began his real education.
In the shop, between jobs, he had time to look
at the books that came in and to begin reading
some of them. As Faraday said to a friend
many years later, the two most influential
things he read at this time were parts of the
Encyclopaedia Brittanica and Jane Marcet's
Conversations on Chemistry.
I entered the shop of a bookseller and
bookbinder at the age of 13, in the year 1804,
remained there eight years, and during the
chief part of the time bound books. Now it was
in those books, in the hours after work, that I
found the beginning of my philosophy. There
were two that especially helped me, the
"Encyclopaedia Brittanica," from which I
gained my first notions of electricity, and Mrs.
Marcet's "Conversations on Chemistry," which
gave me my foundation in that science. . . .
Faraday to A. De la Rive
2 September 1858
SCIENTIST AND PUBLIC FIGURE
Humphry Davy
For a young man, like Michael Faraday,
interested in chemistry and electricity, no one
could have been more exciting to see or hear
than Humphry Davy. Easily the most popular
scientific lecturer of his time, Davy was
appointed Professor of Chemistry at the Royal
Institution when he was only 24. His reputation
rested not only on his lectures and his
handsome good looks (he was long London's
most eligible bachelor), but also on solid
scientific work. Not only was he the great
pioneer of electrochemistry, but he also
invented the miner's safety lamp, wrote a
treatise on agriculture, and made contributions
to the young science of geology. At age 33, in
1812, Davy was knighted for his work, and in
the following year he made what some said
was his greatest discovery, Michael Faraday.
Lecturing at the Royal Institution. Burndy Library
The Royal Institution
The Royal Institution of Great Britain was
founded in 1799 largely through the efforts of
American born Benjamin Thompson, Count
Rumford. Still housed in its original building at
21 Abermarle Street in London, the Institution
was from the beginning devoted both to
popular lectures on scientific and useful
subjects and to laboratory investigation of
important scientific problems. In Faraday's
time, admission was by ticket only, and it was
due to the generosity of one of his employer's
customers that he got his first chance to hear
a lecture by Humphry Davy, the Institution's
popular Professor of Chemistry. Just a year
later, in 1813, Faraday took the job of Davy's
laboratory assistant, and thus began a career
at the Royal Institution that was to last more
than fifty years.
Faraday’s notes on Humphry Davy’s lectures.
courtesy AIP Niels Bohr Library.
Royal Institution,
Humphry Davy.
Burndy Library
SCIENTIST AND PUBLIC FIGURE
Davy’s Assistant
Faraday the Scientist
As the young Faraday worked through the
years of his apprenticeship in book-binding,
he found time to pursue chemical experiments,
engage other amateurs in lively scientific
debates, and attend whatever scientific
lectures were free to a London workingman. In
the year 1812, as the apprenticeship drew to a
close, Faraday determined that he did not want
a life as a binder, but that his future belonged
in science. Some months after he attended
four of Humphry Davy's Royal Institution
lectures, he had the chance to show his careful
notes of the lectures and accompanying
drawings to Davy, who was flattered and
impressed by them. Davy had no job to offer
Faraday at that time, but a few moths later, in
February 1813, his laboratory assistant (or
"fag and scrub", as he was called) was
dismissed for brawling. When Faraday was
offered the opening, he leaped at the chance,
and within weeks was deeply immersed in the
work of one of the finest chemical laboratories
of the day.
Faraday's position at the Royal Institution
gave him the finest education in experimental
science that was possible. After only a few
years of helping Humphry Davy, Faraday was
put in charge of all the laboratory and lecture
apparatus of the Institution. He became a wellknown analytical chemist, doing important
work on steel and glass and discovering new
compounds, such as benzene. In 1824, he was
made a Fellow of the Royal Society and in the
following year was appointed Director of the
Laboratory of the Royal Institution. In 1826 he
began the Institution's famous series of
"Friday Evening Disclosures" to communicate
the newest scientific discoveries to the public,
and later he started a series of scientific
lectures for children, which are still popular
Christmas time events in Britain. Recognized
as an extraordinary experimental scientist,
Faraday was also the greatest popularizer of
science in history.
Faraday the Man
Faraday's popularity was due not only to his
skill as a lecturer and demonstrator, but also
to the gentleness of his personality. A modest
man, his greatest ambitions were fulfilled by
being able to spend his life in the Royal
Institution's laboratory and lecture hall. The
only thing that matched his preoccupation with
science was his devotion to his wife through a
marriage of 46 years, and a religious faith that
made science for him a humble appreciation of
the wonders of creation.
Young Michael Faraday. Burndy Library
ELECTRICITY AND MAGNETISM
Oersted’s Discovery
Faraday and Ampere
There were strong philosophical currents in
the 18th and 19th centuries that led many
experimenters to believe that all the forces of
nature - light, electricity, magnetism, gravity were all but forms of one basic source. Hans
Christian Oersted, a Danish chemist was one
of those who believed this. Therefore, in 1820,
when he observed a compass needle moving
under the influence of the electric current in a
nearby wire, he was not surprised. He did,
however, understand the importance of his
discovery, and in a matter of months he sent
out to scientists all over Europe his
announcement of the magnetic effects of
electricity. Written in Latin, the announcement
caused a storm of excitement as others rushed
to duplicate the simple experiment.
The correspondence between Faraday and
Ampere began in the early 1820's and
continued for many years. The two got along
very well, but their scientific styles were very
different.
Faraday
was
a
superb
experimentalist who approached his subject
with great intuition and imagination, but he
was very careful in his speculations and
analyzed things in very physical terms.
Ampere, also a fine laboratory scientist, was a
mathematical genius who sought to describe
nature through numbers and abstract symbols.
Faraday's lack of mathematical training always
limited
his
appreciation
of
the
accomplishments of theorists like Ampere. A
letter from Faraday to Ampere, written in
1825, voices the complaint, "With regard to
your theory, it so soon becomes mathematical
that it quickly gets beyond my reach. . . ."
Electromagnetism
Hans
Christian
Burndy Library
Oersted.
Andre Marie Ampere.
Burndy Library
Ampere
One of the many scientists who hastened to
study the phenomenon discovered by Oersted
was Andre Marie Ampere, Professor of
Mechanics at the Ecole Polytechnique in Paris.
Ampere extended the investigation of the
magnetic effects of electricity to include the
interaction between two current-carrying
wires, which he showed to be the same as that
between a wire and a magnet. Through an
extraordinary series of careful experiments,
Ampere established the foundations of the
science of electrodynamics - the study of the
relationship between electric, magnetic and
mechanical phenomena, earning himself the
title, "the Newton of electricity."
While the magnetic effects of electric
currents were something that many besides
Oersted had suspected, the nature of these
effects was surprising. What astonished many
was the circular nature of the magnetic
influence of a current-carrying wire. All other
such influences in nature had been observed to
be linear.
ELECTROCHEMISTRY
Volta’s Pile
Davy and Electrochemistry
The first years of the 19th century were an
exciting period in the history of electricity
largely due to the discovery of Alessandro
Volta, an Italian physicist. In 1800, Volta
announced that he had found a new source of
electricity - what we call the battery. Before
that time, the only important means of
generating electricity was by friction, as in the
creation of static electricity by rubbing fur or
hair. Volta showed how to construct a "pile" of
discs, alternating silver and zinc, separated by
pieces of moistened cloth, to create a source
of electric current. The Voltaic pile caused a
sensation and quickly became an indispensable
tool for a vast number of new experiments.
No one made better use of Volta's pile than
Humphry Davy at the Royal Institution. There
Davy constructed a giant "battery" of piles
which he then used in a variety of dazzling
experiments. Since Davy was convinced that
the source of Voltaic electricity was a
chemical reaction, he proceeded to show how
it, in turn, could cause other reactions. His
most important results were the discovery, by
electrolysis, of hitherto unknown chemical
elements,
including
sodium,
potassium,
calcium, and magnesium. Learning from Davy,
Faraday himself became skilled at electrolysis,
and, much later (in 1834), discovered the laws
that describe the relationship between the
amount of a substance decomposed and the
quantity of electricity used.
Volta’s Pile
Allesendro Volta. Burndy Library
THE SEARCH FOR RELATIONSHIPS
After Oersted
Assisted by the Voltaic cell, and spurred on
by Oersted's discovery of electromagnetism, in
the 1820's scientists throughout Europe and in
America explored the nature of electricity and
its relationship with other forces. In France,
Francois Arago discovered the magnetic effect
of a rotating copper disc, a mysterious
phenomenon explained years later by Faraday.
In England, Charles Babbage, famous as the
pioneer of the digital computer, attempted to
explain Arago's effect in terms of Ampere's
electrodynamics. And in Germany, Georg
Simon Ohm performed the experiments that
led to the statement of his law, relating the
current in a wire to the electromotive force
(voltage) and the resistance in the circuit.
Francois Arago. Burndy Library
THE SEARCH FOR RELATIONSHIPS
Faraday's Rotator
Charles Babbage.
Burndy Library
George Simon Ohm.
Burndy Library
In America
The excitement over electromagnetism was
not confined to Europe, but it stirred up
interest in the small scientific community of
the United States. Unquestionably the most
important American experimenter was Joseph
Henry, who in the late 1820's was a teacher of
mathematics and science in Albany, N.Y.
Henry learned how to greatly increase the
power of electromagnets, and was one of the
first to seek practical uses for them. In 1831,
he devised the first electromagnetic telegraph
and carried out experiments that led him to the
independent discovery of electromagnetic
induction. Due to his failure to publish his
discovery, he never received the same
recognition as Faraday. Henry later became
the first Secretary of the Smithsonian
Institution in Washington.
Among the scientists who turned their
attention to the investigation of Oersted's
electromagnetism
was
Michael
Faraday
himself. It did not take Faraday long to make
an extraordinary contribution of his own - the
first electric motor. Intrigued by the apparent
circular nature of electromagnetic effects,
Faraday constructed a "rotator", consisting of
a magnet stuck upright in a cup of mercury,
with a current-carrying wire hanging down
from above, with one end in the mercury.
When the circuit of the wire, mercury, and
battery was completed, the wire began
rotating around the magnet. Faraday also
demonstrated that a magnet could be made to
rotate similarly around a wire. It was more
than 50 years before a practical electric motor
was
invented,
but
Faraday
clearly
demonstrated the principle.
Faraday’s rotator. National Museum of American History, Smithsonian
Institution
Thermoelectricity
Joseph Henry. Burndy Library
The widespread belief that all the forces of
nature were related to one another was given
powerful support by the discovery of
electromagnetism. This spurred the search for
further relationships. In 1821, the German
Thomas Johann Seebeck discovered a
connection between electricity and heat by his
observation of what is known as the "Seebeck
effect." In this instance of thermoelectricity,
heat applied at the junction of two different
metals causes a current to flow. This is the
principle applied in the thermocouple, which is
used for very accurate measurements of
temperature.
Seebeck
announced
his
discovery in a paper published in 1823.
THE GREAT EXPREIMENTALIST
Faraday in the Laboratory
The Apparatus
Faraday's motto was "Work, Finish,
Publish." No scientist in the 19th century
excelled Faraday in the laboratory, for there
he combined superb technique with a
scientific intuition that was the wonder of his
colleagues. His training as an analytic
chemist under Humphry Davy, added to the
natural ability he had shown even as a bookbinder, gave him skills at physical
manipulation in the laboratory that were
unmatched. To these skills he added
extreme care in making and recording his
observations, as his laboratory notes show.
Equally important, he brought to his work a
fruitful yet disciplined imagination, shunning
wild speculation but always receptive to
well-argued new ideas.
Faraday's laboratory at the Royal Institution
was a well-equipped one, but his most important
experiments were done with very simple
devices. The crucial work that he did in the
summer and fall of 1831, leading to the
discovery of electromagnetic induction, was
done with a simple ring of soft iron, wrapped
with copper wire, with a trough battery
supplying current and a compass needle as a
meter. Another important device consisted of a
paper cylinder wrapped with copper wire and
connected to a galvanometer. With these simple
tools, Faraday revolutionized electrical science.
The originals are still preserved at the Royal
Institution in London.
Faraday in the laboratory at the Royal Institution. Royal Institution, courtesy AIP Niels Bohr Library.
THE GREAT EXPREIMENTALIST
Faraday’s induction ring. Royal Institution, courtesy AIP Biels Bohr
Library
Using a Magnet
Faraday’s coil and magnet. Royal Institution, courtesy AIP Niels Bohr
Library
The Crucial Experiments
Between 1821, when he invented his rotator,
and 1831, Faraday was too busy with other
matters
to
give
much
attention
to
electromagnetism. In August of 1831, however,
he undertook experiments to test some notions
he had about the nature of electricity. He
rejected the idea that electricity consisted of a
fluid or a stream of particles, but the action of his
rotator convinced him that something must move
through a wire. Some experiments on sound
suggested to Faraday that electricity might
consist of vibrations moving through matter.
If this were so, Faraday reasoned, perhaps he
could cause the vibrations in one currentcarrying wire to set up similar vibrations in a
nearby, but separate, wire. Thinking that these
vibrations might be intensified by acting through
an electromagnet, he made one out of an iron ring
wrapped with wire on one side. On the other side
of the ring, he wrapped another coil of wire,
which he attached to a galvanometer (simply a
compass with a wire connected). When, on
August 29th 1831, he connected the first side of
the ring to a battery, he was watching the
galvanometer needle - it jumped, then returned
to normal. On disconnecting the battery, the
needle jumped again. By starting or stopping a
current in the first wire, he had induced, for an
instant, a current in the second wire. Faraday had
made a great discovery, but it was only the
beginning of his work, not the end.
Faraday quickly realized that his ring
experiment not only supported his notions about
electricity, but it also revealed something about
the
relationship
between
electricity
and
magnetism. Faraday embarked on a series of
experiments to further clarify this relationship.
The most important of these was with a paper
cylinder wound with several coils of copper wire,
connected to a galvanometer. When Faraday
thrust a bar magnet into the hollow of the
cylinder, the meter's needle jumped, then when
he pulled the magnet out, the needle jumped
again, but in the opposite direction. Induction did
not require the creation of a magnet (as in the
ring experiment), but was caused simply by
moving a magnet near a wire. This was truly, in
Faraday's words, "the production of electricity
from magnetism."
Reporting the Results
Faraday was well aware that he had made a
very important discovery, but he also knew that
he did not understand what he had found. He
therefore took time over the next few months to
experiment and further work out his ideas.
Finally, in late November, 1831, he felt he knew
enough to announce his findings to the Royal
Society. He then wrote a letter to Richard
Phillips, one of his best friends, explaining the
research program that he had set out for himself,
the results of which were to appear as his
Experimental Researches in Electricity over the
next twenty years. To Phillips, Faraday would
confess that "It is quite comfortable to me to find
that
experiment
need
not
quail
before
mathematics, but is quite competent to rival it in
discovery."
INTERPRETATION AND APPLICATION
Lines of Force
Experimental Researches
While Faraday was always careful in his
theorizing, he did not shrink from attempting to
explain the effects he discovered. In his first
report to the Royal Society on electromagnetic
induction, in November 1831, he proposed a
number of concepts to help explain how
magnetism could produce electricity. The most
important of these was the idea of magnetic
"lines of force". An electric current was
produced, Faraday suggested, when a conductor
passed across these lines of force. Furthermore,
it seemed that the direction and strength of the
current depended in the direction and speed of
the relative motion of the conductor and the lines
of force. This turned out to be one of the most
powerful ideas in all electrical science, though its
true power was only realized by James Clerk
Maxwell more than thirty years later.
Faraday's announcement to the Royal Society
in November 1831 of his discovery of
electromagnetic induction was the first of the
long series of papers that were collected
together and printed as Experimental Researches
in Electricity. In their final form, the Experimental
Researches filled three volumes, which became
the bible of electrical science for most of the
nineteenth century, guiding such disparate
figures as John Tyndall, Faraday's successor at
the Royal Institution, and Thomas Edison, to
whom Faraday was the "Great Experimenter."
A New Source of Electricity
In the course of his experiments in the Fall of
1831, Faraday asked himself this question: if he
could produce a momentary current by moving a
magnet in and out of a coil of wire, was there a
way to produce a continuous current? Faraday
ingeniously devised a way, rigging up a copper
disc that rotated between the poles of a large
magnet. When the disc was turned, a wire was
applied to its edge and another to the axis. A
meter between the wires revealed that a steady
current was being produced. Faraday had
invented the electric generator -- one of the
most important discoveries in the history of
technology.
Faraday’s first generator, Burndy Library
INTERPRETATOIN AND APPLICATION
Faraday on Electric Waves
I am inclined to compare the diffusion of
magnetic forces from a magnetic pole to the
vibrations upon the surface of disturbed water, or
those of air in the phenomenon of sound, i.e., I
am inclined to think the vibratory theory will
apply to these phenomena as it does to sound,
and most probably light.
in observations deposited
at the Royal Society
12 March 1832
Faraday’s Experimental Researches in Electricity from the copy
belonging to John Tyndall. Burndy Library
APPRECIATION
An Engineer on Faraday
Perhaps the greatest discovery of Faraday's
long career of scientific research was that of
electromagnetic induction in the year 1831. . . .
Faraday's discovery was a great step; it revealed
the action of magnetic force in apparently empty
space, it inaugurated that deeper insight into the
mechanism, still only dimly guessed, which
connects matter with all other matter in space;
and it invested the all pervading ether with a
dignity and power that in the hands of many great
men since his time, has probably paved the way
for our future comprehension of magnetism,
gravitation, and radiant energy. . . . The
development of this discovery of electromagnetic induction had practically created
electrical engineering."
Arthur E. Kennelly
Trans. AIEE, 1890
A Scientist on Faraday
When we consider the life work of Faraday it is
clear that his researches were guided and
inspired by the strong belief that the various
forces of nature were inter-related and
dependent on one another. It is not too much to
say that this philosophic conviction gave the
impulse and driving power in most of his
researches and is the key to his extraordinary
success in adding to knowledge.
The more we study the work of Faraday with
the perspective of time, the more we are
impressed by his unrivalled genius as an
experimenter and natural philosopher. When we
consider the magnitude and extent of his
discoveries and their influence on the progress of
science and industry, there is no honor too great
to pay to the memory of Michael Faraday - one
of the greatest scientific discoverers of all time.
Lord Rutherford
1931
Faraday's Place in History
Michael Faraday was one of the most
respected and admired scientists of his day. Held
in high regard by his colleagues, his skill as a
lecturer and his life-long dedication to spreading
the gospel of science to all earned him a
widespread popular appeal. His humility led him
to refuse some of the honors that might have
been his, but he was, in his last years, given a
house rent-free by Queen Victoria. There he
died in 1867.
The place of Faraday in the history of science
and technology is best described by scientists
and engineers themselves. In particular, all those
who studied and applied electricity in the
following years found themselves in Faraday's
debt.
APPRECIATION
Faraday's Place in Science and Technology
Faraday and Maxwell
His identification with the discovery of
electromagnetic induction would be monument
enough for a humble man like Michael Faraday,
but we owe much more than that to him.
Faraday's Laws are the most fundamental
principles of electrochemistry. The Faraday
Effect, in which he showed how a magnetic field
affected
polarized
light,
was
the
first
experimental clue to the electromagnetic nature
of light. His experiments in 1833 on the
conductivity of silver sulfide provided the first
glimpse at the wonderful properties of semiconductors, the materials at the heart of
transistors and all microelectronics. Statues,
plaques and medals honor the man in many
places, but the electrical engineers' own token of
esteem was created in 1891, when the
International Electrical Congress voted to name
the electrical unit of capacitance the Farad in his
honor.
Even in his later years, in failing health and
memory, Faraday kept up a widespread
correspondence with the leading scientists of his
time. He also paid generous attention to the
younger generation of scientists, even though his
lack of formal training, especially in mathematics,
often limited his appreciation of their work.
James Clerk Maxwell was only 26 when his often
highly abstract work elicited this response from
Faraday:
When a mathematician engaged in investigating
physical actions and results has arrived at his
conclusions, may they not be expressed in
common language as fully clearly and definitely
as in mathematical formulae? If so, would it not
be a great boon to such as I to express them so translating them out of their hieroglyphics that
we also might work upon them by experiment.
LINES AND FIELDS
The Pursuit of Theory
The Debate on Lines of Force
Faraday continued to develop and extend his
concept of lines of magnetic or electric force in
the 1830's and 1840's. Because this concept was
not mathematical, however, and seemed to be
crudely intuitive, it was rejected by most
scientists. There were two important exceptions,
however: William Thomson and James Clerk
Maxwell. Thomson (who was later made Lord
Kelvin) was born in Belfast, Ireland, in 1824, and
after excelling as a student of mathematics and
physics, he became a professor at the University
of Glasgow, where he stayed for more than fifty
years. In 1845, Thomson published a paper
showing how Faraday's lines of force could be
interpreted mathematically, and he subsequently
showed how Faraday's concepts of magnetic and
electrostatic force could be treated analogously
to theories of heat and mechanics, thus laying the
mathematical foundations of field theory.
In one of the last scientific papers of his life,
Faraday acknowledged the debate over his ideas,
and recognized the assistance he had received
from supporters like Thomson:
The attention of two very able men and
eminent mathematicians has fallen upon my
proposition to represent the magnetic force; and
it is to me a source of great gratification and
much encouragement to fin that they affirm the
truthfulness and generality of the method of
representation.
APPLICATION
Application
The practical implications of Faraday's
discovery of electromagnetic induction in 1831
were quickly recognized. Only a year later,
Hyppolyte Pixii, in France, devised the first
effective electric generator. Within a decade, in
the 1840s, generators were being used for
electroplating. In the 1850s, the first efforts were
made to apply them to electric lighting, using
bright, glaring arc lights. Skeptical at first,
Faraday himself was finally persuaded that they
would be useful in lighthouses.
Electroplating works, with generator, 1840s. National Museum of
American History, Smithsonian Institution.
Model of Pixii generator, National Museum of American History,
Smithsonian Institution
Generator for arc lighting, 1085s.
National Museum of American History,
Smithsonian Institution
BEGINNINGS
John Clerk Maxwell. Courtesy Prof. C.W.F. Everitt.
Glenlair. Courtesy Prof. C.W.F. Everitt
Origins
James Clerk Maxwell was born in Edinburgh,
Scotland on the 13th of June, 1831. The Clerk
Maxwells (that was the family name) were
comfortably well-off land owners, and John Clerk
Maxwell, James' father, was an educated man,
trained in the law and interested in science and
invention. Since his mother died when he was
only eight, his father had great influence on the
young Maxwell's education, and provided
considerable encouragement for his scientific
bent.
Childhood
Maxwell's childhood years were divided
between Edinburgh and the family estate of
Glenair, in the Galloway region of Scotland. At
Glenair, Maxwell spent his boyhood in a fashion
typical of more liberal landed gentry of the day.
His most important companion was his cousin,
Jemima Wedderburn, and it is thanks to her that
we possess such a charming picture of the more
comfortable aspect of life in rural Scotland in the
middle of the 19th century. Both she and James
Clerk Maxwell himself proved to be talented
sketchers, as shown by these examples of her
work.
Pictures by Jemima Wedderburn,
From the collection of
Briggadier John Wedderburn-Maxwell
Courtesy of Prof. C.W.F. Evereitt
GENTLEMAN AND SCHOLAR
Education
The Gentlest of Men
Education was valued highly in the Scotland of
Maxwell's youth, and he had the advantage of the
best Edinburgh could offer. He began to show
signs of brilliance as a student at the Edinburgh
Academy, and had a paper read before the Royal
Society of Edinburgh when he was 14. At age 16,
he entered the University of Edinburgh, where he
first began to direct his attention to physics.
Finally, in 1850, he entered the University of
Cambridge, where, as a student at Trinity
College, he was exposed to the finest
mathematical and scientific minds in Britain. At
Cambridge, Maxwell acquired the scientific
sophistication and academic polish that permitted
him to move quickly into the most elevated
circles of British science.
Few men have so combined high intellectual
achievement with a reputation for gentle
character and rich good humor as James Clerk
Maxwell. Short of stature and hesitant of speech,
Maxwell nonetheless made a deep impression on
those around him. His devotion to his wife and his
quiet religious faith were aspects of his humble
side. The exuberant good humor that shows in
his poetry (which he wrote throughout his life)
shows, however, that he was anything but dour.
Professor Maxwell
Unlike some other great scientists of his time,
like Faraday and William Thomson, Maxwell's
academic career took him to many places. Soon
after leaving Cambridge he became Professor of
Natural Philosophy in Aberdeen, Scotland. In
1860, he moved to London as a professor at
King's College, but after five years he moved
back to Scotland to take care of the family estate.
Finally, in 1871, he was appointed the first
Cavendish Professor of Experimental Physics at
Cambridge, and there he devoted his time to
building up the new Cavendish Laboratory, which,
by the time of Maxwell's death in 1879, was on
its way to becoming one of the foremost physics
laboratories in the world.
Maxwell as a student at Cambridge, 1855. Burndy Library
GENTLEMAN AND SCHOLAR
Excerpts from a Poem
Written while a Student at Cambridge
Deep St. Mary's bell has sounded,
And the twelve notes gently rounded
Endless chimneys that surrounded
My abode in Trinity.
(Letter G, Old Court, South Attics),
I shut up my mathematics,
That confounded hydrostatics Sink it in the deepest sea!
In the grate the flickering embers
Served to show how dull November's
Fogs had stamped my torpid members,
Like a plucked and skinny goose.
And as I prepared for bed, I
Asked myself with voice unsteady,
If of all the stuff I read, I
Ever made the slightest use.
from "A Vision," 1852
Valentine by a Telegraph Clerk
to a Telegraph Clerk
"The tendrils of my soul are twined
With thine, though many a mile apart,
And thine in close-coiled circuits wind
Around the needle of my heart.
"Constant as Daniell, strong as Grove,
Ebullient through its depths like Smee,*
My heart pours forth its tide of love,
And all its circuits close in thee.
"O tell me, when along the line
From my full heart the message flows,
What currents are induced in thine?
One click from thee will end my woes."
Through many an Ohm the Weber flew,
And clicked this answer back to me, -"I am thy Farad, staunch and true,
Charged to a Volt with love for thee."
*Daniell, Grove and Smee are types of batteries
used by telegraphers.
Maxwell, his wife, Katherine Mary Dewar, and their dog, Toby.
Courtesy Prof. C.W.F. Everitt
Maxwell about the time he became Professor at Cambridge, 1872.
Courtesy Prof. C.W.F. Everitt.
SATURN’S RINGS
Saturn’s rings as taken by Voyager I. Courtesy NASA Jet Propulsion Laboratory.
What are Saturn's Rings?
The Power of Physics
When, in 1610, Galileo first pointed a telescope
toward Saturn, he saw what appeared to be little
stars attached to the side of the planet. Almost
50 years later, the Dutch scientist Christian
Huygens discovered that these were in fact rings
circling Saturn. Since that time, Saturn's rings
have fascinated observers, and have posed a
riddle -- what are they? Now, in the 1980's,
thanks to the Voyager space probes, we can see
for ourselves that the rings are made of millions
of particles, ranging in size from dust to many
meters in diameter. In this result, at least,
Voyager's wonderful pictures came as no
surprise, because scientists have believed for
more than 100 years that the rings were made of
particles, thanks not to an astronomer, but to a
mathematical physicist, James Clerk Maxwell.
When Maxwell was still a Fellow at Cambridge,
he wrote a paper, "On the Stability of the Motion
of Saturn's Rings," which the Astronomer Royal
of England described as "one of the most
remarkable applications of Mathematics to
Physics that I have ever seen." Here, Maxwell
showed that the only structure of Saturn's rings
that was consistent with the accepted laws of
mechanics was "one composed of an indefinite
number of unconnected particles." Maxwell
achieved this result by skillful mathematical
analysis, but he then, typically, went on to
illustrate his argument with a model, which can
still be seen in the Cavendish Laboratory,
Cambridge.
MAXWELL AT WORK
Color and Optics
Maxwell's chief contributions to science were
based on his mathematical skills and his ingenuity
in applying them to physics. He was never
without an interest in experiment, however, and
he distinguished himself in several areas with his
experimental work. For his work on color
perception, Maxwell was awarded the Rumford
Medal of the Royal Society in 1860. In these
experiments he constructed a number of devices,
including a "color wheel" and a "color box," that
allowed him to see how mixtures of different
colors were perceived by different people. His
most important collaborator in this work was
Katharine Mary Dewar, his wife. Maxwell's work
constituted the beginnings of the science of
quantitative colorimetry. Related achievements in
this area included making the first true color
photograph, which he displayed to Faraday and
others at the Royal Institution in 1861, and
inventing the "fish-eye" lens.
Thermodynamics
Maxwell's Experimental Method
There is a tradition in Trinity that when I was
here I discovered a method of throwing a cat so
as not to light on its feet, and that I used to throw
cats out of windows. I had to explain that the
proper object of research was to find how quick
the cat would turn round, and that the proper
method was to let the cat drop on a table or bed
from about two inches, and that even then the cat
lights on her feet.
Maxwell writing to his wife, 1870
The field of science, beside electromagnetism,
with which Maxwell's name is most closely
associated, is thermodynamics, or, more
precisely, the study of the motion of molecules.
Here, Maxwell's contribution consisted of both
mathematical
analysis
and
experimental
observations. Beginning with Rudolf Clausius'
work on the kinetic theory of gases, Maxwell was
one of the primary figures in the development of
statistical mechanics - the analysis of the
behavior of large numbers of molecules. To point
out the statistical nature of the second law of
thermodynamics (which says that heat can never
pass on its own from a colder to a warmer body),
he invented "Maxwell's demon" - the fantastic
creature that would be necessary to sort out fast
and slow molecules in a gas.
ELECTRICITY: SCIENCE AND ENGINEERING
Maxwell on Thomson
I was aware that there was supposed to be a
difference between Faraday's way of conceiving
phenomena and that of the mathematicians, so
that neither he nor they were satisfied with each
other's language. I had also the conviction that
this discrepancy did not arise from either party
being wrong. I was first convinced of this by Sir
William Thomson, to whose advice and
assistance, as well as to his published papers, I
owe most of what I have learned on the subject.
Maxwell, Treatise on Electricity and
Magnetism, 1873
Galvanometers and Recorders
Lord Kelvin, National Museum of American History,
Smithsonian Institution.
William Thomson, Lord Kelvin
Foremost
among
William
Thomson's
contributions to electrical engineering and to the
success of submarine telegraphy were the
instruments he invented for receiving the very
weak signals that emerged from a cable over
2,000 miles long. Thomson's mirror galvanometer
was the first satisfactory receiver, and was so
sensitive that it clearly registered a round-trip
transatlantic signal powered by a thimble-sized
battery. Later, his siphon recorder proved to be
even more sensitive and had the advantage of
making a permanent record on paper of signals
received.
No scientist had greater influence on Maxwell's
work on electricity than William Thomson. It was
Thomson, like Maxwell a graduate of Cambridge,
who provided a glimpse of the possibilities
inherent in Faraday's concept if lines of force. He
also made important contributions to magnetic
theory and wrote one of the earliest studies of
electrical oscillations (using a Leyden jar).
Thomson was one of the most honored scientists
of his day, due largely to his contributions to
electrical engineering. He applied himself to
many of the problems that arose with attempts to
lay a telegraphic cable under that Atlantic
between Britain and America. The ultimate
success of the Atlantic cable in 1866 owed much
to Thomson, who accompanied the cable layers
aboard the ship, Great Eastern. Thomson was
elected president of the Royal Society and three
times president of the Institution of Electrical
Engineers.
Kelvin’s mirror galvanometer. National Museum of American History,
Smithsonian Institution.
ELECTRICITY: SCIENCE AND ENGINEERING
Maxwell's Practical Side
Maxwell was much less interested in
engineering problems than William Thomson, but
he did make contributions in at least one area -standards. As a member of a Committee
organized by the British Association (at the
suggestion of Thomson) to determine a standard
unit of electrical resistance Maxwell was
particularly useful. While a professor at King's
College, London, Maxwell joined with others to
make the fundamental measurements needed to
define the ohm, the unit of electrical resistance.
The British Association standard ohm. National Museum of American
History, Smithsonian Institution.
MAXWELL’S EQUATIONS
Maxwell's Equations
A Theory in Mathematical Form
To the question, "What is Maxwell's theory?", I
know of no shorter or more definite answer than
the following: Maxwell's theory is Maxwell's
system of equations.
Heinrich Hertz, 1891
Maxwell's greatest work was his contribution
to electromagnetic theory. As stated by Heinrich
Hertz, who helped confirm Maxwell's predictions,
the theory was embodied in Maxwell's famous
equations of the electromagnetic field. These
equations were mathematical interpretations of
Faraday's concepts, transforming the ideas about
lines of force into precise formulas. Out of this
transformation emerged a new picture of the
relationship between electricity and magnetism.
And from Maxwell's propositions about how
electricity and magnetism were propagated
through space came a startling new theory of
electromagnetic waves, seen in their most
familiar form as light.
Electric Force
An electric charge is a source of an electric
field. In terms more familiar to Faraday, this
equation says that electric lines of force begin
and end on electric charges (though this is not
necessarily true in a changing magnetic field).
MAXWELL’S EQUATIONS
Magnetic Force
There are no such things as "magnetic
charges," therefore, magnetic lines of
force always form closed loops (and never
diverge from a point source).
Electromagnetic Induction
Voltage is generated in a conductor as
it passes through a magnetic field (or cuts
magnetic lines of force). This was
Faraday's great discovery of 1831.
Magnetic Effect of Electric Current
An
electric
current
is
always
surrounded by a magnetic field (or lines of
force). This was the conclusion that
Faraday had derived from Oersted's
experiment.
There are many ways of writing Maxwell’s equations.
The important symbols in the forms use here are:
D = electric flux density
ρ = electric charge density
B = magnetic flux density
H = magnetic intensity
E = electric field strength
V is a “vector operator”, indicating that the equations
refer to conditions in all directions in space.
INTERPRETING FARADAY
On Faraday's Lines
Maxwell on Faraday
Most 19th century physicists rejected Michael
Faraday's concept of lines of magnetic force. The
idea seemed too fuzzy and crude to
mathematically trained men, who felt comfortable
only with motions and forces that could be
precisely measured. Maxwell, however, after
reading the work of William Thomson and of
Faraday himself, believed that the lines of force
did indeed represent something real. He then set
out to show how Faraday's intuitive concept
could be put into mathematical form. Beginning in
1856, with his paper "Faraday's Lines of Force",
Maxwell produced a long series of articles which
were to revolutionize ideas about electricity,
magnetism, and light. In these papers he carefully
explored the implications of Faraday's ideas,
developed analogies and models to show how
these ideas related to more familiar concepts,
and
finally
formulated
the
mathematical
expressions that made up his famous equations.
As I proceeded with the study of Faraday, I
perceived that his method of conceiving the
phenomena was also a mathematical one, though
not exhibited in the conventional form of
mathematical symbols. I also found that these
methods were capable of being expressed in the
ordinary mathematical form, and thus compared
with those of the professed mathematicians.
Treatise on Electricity and Magnetism, 1873
Mathematical and Mechanical Reality
It was widely accepted in the middle of the
19th century that there was a fundamental
difference in the descriptions of nature used by
mathematicians and those with a more purely
physical outlook. This is one of the reasons that
Faraday's theoretical ideas were not closely
looked at by mathematicians. The work of
Maxwell changed all of this. He said that one of
the reasons for his studies in electromagnetism
was to demonstrate that the gap that others
perceived between the intuitive notions of
Faraday and the mathematical approach found in
the universities could be bridged. Not only did
Maxwell succeed in closing this gap, but his work
later became the key influence in extending the
application of mathematical analysis beyond the
boundaries of science and into the realm of
engineering.
The Treatise
Maxwell in 1868. Courtesy of Prof. C.W.F. Everitt
Maxwell's
Treatise
on
Electricity
and
Magnetism appeared in 1873. It represents the
one effort that Maxwell made to bring all of his
ideas about electricity and magnetism together in
a single work, and its influence was enormous.
Almost all the elements of Maxwell's theory had
appeared in his earlier papers, but the Treatise
allowed scientists to see his ideas as parts of a
complete (if not polished) theory.
Even for scientists, however, the Treatise was a
very difficult book, and for others it was largely
incomprehensible. It required decades, therefore,
for
the
true
importance
of
Maxwell's
accomplishment to become generally known and
appreciated.
ELECTRICITY AND LIGHT
The Electromagnetic Nature of Light
The Speed of Light
...we have strong reason to conclude that light
itself -- including radiant heat, and other
radiations if any -- is an electromagnetic
disturbance in the form of waves propagated
through the electromagnetic field according to
electromagnetic laws.
The first serious efforts to determine the speed
of light were made in the 17th century, and
beginning in the middle of the 19th century very
careful measurements were made by a number of
experimenters. After Maxwell pointed out the
correlation between the figures for the speed of
light
and
those
for
the
electromagnetic/electrostatic
ratio,
many
measurements were made of both in an effort to
confirm experimentally their agreement.
Maxwell, "Dynamical Theory of the
Electromagnetic Field," 1864
Electromagnetic Waves
The most wonderful product of Maxwell's
interpretation of Faraday was his conclusion that
electrical and electromagnetic phenomena acted
through waves. Like Faraday, Maxwell rejected
the common notion that these phenomena were
the product of forces that acted instantaneously
between bodies at a distance, with no intervening
medium. Instead, Maxwell said that there was a
medium -- an "ether" -- that surrounded
everything, filling all space, even a vacuum.
Electricity acted through disturbances in this
medium, disturbances that traveled in the form of
waves. Using his equations, he showed that all
such waves must be both electrical and magnetic
in nature and that the speed with which the wave
travels is equal to the ratio between the
electrostatic and the electromagnetic units in
which a given quantity of electricity is measured.
This ratio was already known from experiment to
yield a speed of about 300,000,000 meters per
second.
This value was so close to the accepted figure
for the velocity of light that Maxwell wrote in a
long letter to Faraday (1861):
I think we now have strong reasons to believe,
whether my theory is a fact or not, that the
luminiferous and the electromagnetic medium are
one. . . .
DATE
INVESTIGATOR
1849
1856
1862
1868
1869
1872
1878
1879
1879
1880
1882
Fizeau
Weber & Kohlrausch
Foucault
Maxwell
Wm. Thomson & King
M’kichan
Comu
Ayrton & Perry
Michelson
Shida
Newcomb
OPTICAL
ELECTRICAL
(X 10’ meters/sec.)
3.153
3.107
2.98
2.842
2.808
2.896
3.004
2.960
2.9991
2.995
2.9984
Implications
The implications of Maxwell's theory of
electromagnetic waves and his identification of
light with these waves were enormous. It took
many years, however, for many of Maxwell's
concepts to be widely accepted and for the
implications to be worked out. One thing
suggested by the theory was that there should
exist electromagnetic waves of a form other than
light -- of the same speed but differing in
frequency and wavelength. It took more than two
decades after Maxwell's first prediction of these
waves before they were detected by the German
physicist, Heinrich Hertz. Another result of
Maxwell's theory was that it focused attention on
his
electromagnetic
medium,
the
ether.
Experimental efforts to detect the ether, such as
those of the American physicist Albert A.
Michelson, led to such anomalous results that
many physicist were thrown into confusion, only
to be rescued by Albert Einstein's special theory
of relativity, published in 1905.
APPRECIATION
Albert Einstein on Maxwell
The greatest alteration in the axiomatic basis
of physics -- in our conception of the structure
of reality -- since the foundation of theoretical
physics by Newton, originated in the researches
of Faraday and Maxwell on electromagnetic
phenomena.
A Radio Man on Maxwell
The whole system of wireless telegraphy is a
development of the original and surprising theory
of Clerk Maxwell, embodying in mathematical
form the experimental researches of Faraday.
Sir Oliver Lodge
A Physicist on Maxwell
His name stands magnificently over the portal
of classical physics, and we can say this of him;
by his birth James Clerk Maxwell belongs to
Edinburgh, by his personality he belongs to
Cambridge, by his work he belongs to the whole
world.
Max Planck
Recognition
James Clerk Maxwell was highly regarded by
scientists of his day, for his mathematical
brilliance was apparent to everyone. He had no
popular following like Faraday, however, for he
was not a particularly good lecturer. He did not
seek the public eye like William Thomson, and
thus was not sought out by engineers and
industrialists. Up to his death at the age of 48 in
1879, Maxwell was known for his devoutness and
modesty, as well as for his fine sense of humor.
Widespread public recognition of his contribution
to science and, thereby, to technology, came only
in the last years of the 19th century, when
confirmations of his theory began to be
commonplace and some glimpses could be seen
of the wonderful uses to which it could be put, in
the form of radio, power generation, and what
was to be known as electronics.
The Cavendish Laboratory, Cambridge. Courtesy Cavendish
Laboratory, University of Cambridge (copyright).
The Cavendish
The most substantial recognition Maxwell
received in his lifetime was his appointment in
1871 as the first Professor of Experimental
Physics at the University of Cambridge. In this
position, he was also the first Director of the
Cavendish Laboratory, which was to become one
of the most famous physics laboratories in the
world. While he was best known for his
theoretical work, Maxwell took seriously the
responsibility of designing the laboratory and
setting up a course of study in experimental
physics. Thanks to Maxwell and his successors,
the Cavendish was for decades the unquestioned
center of British contributions to atomic physics.
One of Maxwell's proudest achievements as
Cavendish Professor was the editing and
publishing of the experimental writings of the
electrical pioneer, Henry Cavendish, whose birth
preceded Maxwell's by exactly a century.
CONFIRMATION
Henry Rowland
Heinrich Hertz,
Burndy Library
Henry A. Rowland,
Smithsonian Institution.
Heinrich Hertz
Unquestionably the most dramatic and
persuasive confirmation of Maxwell's theory of
electromagnetic waves was the detection of
nonoptical waves by Heinrich Hertz between
1886 and 1888. Made Professor of Physics at
Karlsruhe University in Germany at the age of
28, Hertz was one of relatively few European
physicists who believed Maxwell's theory. He had
to solve some very difficult problems in designing
a source (transmitter) of electromagnetic waves,
a detector, and means for confirming the wavelike nature of the phenomena with which he was
dealing. He used the oscillating sparks of an
induction coil and a Leyden jar to produce what
we would call short radio waves. Focusing the
waves with a reflector, he showed their presence
by means of sparks in a wire-loop gap a few
meters away. Further experiments showed that
the "Hertzian" waves behaved just like light -they could be polarized and could show patterns
of interference. And, as was to be shown only a
few years later, they could be used for "wireless"
communications -- radio.
Henry Rowland was one of the first American
physicists to take up the challenge of testing
Maxwell's theory. While spending a year in the
laboratory of the great German physicist, Herman
von Helmholtz, Rowland demonstrated that an
electric charge on a moving body had exactly the
same magnetic effect as an electric current
moving through a conductor, just as Maxwell had
predicted. Later, after he had become Professor
of Physics at the new Johns Hopkins University,
Rowland made very accurate measurements of
the electromagnetic/electrostatic ratio, further
confirming that it was equal to the speed of light.
Further Confirmation
The physicists discussed here were just a few
of those who worked to test Maxwell's theory.
Other predictions that were tested, and
eventually confirmed, included the relationship
between the conductivity of a material and its
reflection of light, the slight physical pressure
that light exerts on things shined upon, and the
relation of light-scattering to reflection and
refraction. The importance of the work done
under the stimulus of Maxwell's theory lay not
only in the confirmation of the theory, but also in
the spur that this work gave to such areas as
optics, solid-state physics, molecular and atomic
theory, and relativity.
Ludwig Boltzmann
While other efforts to confirm Maxwell's
predictions were less spectacular than Hertz's,
they were still important. Another European who
quickly took up Maxwell's ideas was Ludwig
Boltzmann, an Austrian. Throughout his career,
Boltzmann dealt successfully with many of the
same problems that Maxwell studied, especially
in statistical mechanics and electromagnetism.
Maxwell's theory predicted that the influence that
an electric field had on a material, measured by
the "dielectric constant" or "permittivity" of the
material, should be equal to the square of the
refractive index (the measure of how much a
material bends light passing into it). Boltzmann
performed experiments that showed this was
indeed the case for such substances as air,
hydrogen, and carbon dioxide. He reported his
findings in 1875.
Ludwig Boltzmann, Lande Collectin, AIP Niels Bohr Library.
APPLICATION
The Importance of Waves
The Equations in the 20th Century
The discovery of electrical waves has not
merely scientific interest though it was this alone
which inspired it. Like Faraday's discovery of
electromagnetic induction, it has had a profound
influence on civilization; it has been instrumental
in providing methods which may bring all the
inhabitants of the world within hearing distance
of each other and has potentialities social,
educational and political which we are only
beginning to realize."
One measure of Maxwell's achievement is the
extent to which his equations are still a basic part
of the equipment of the electrical engineer. The
design of tools and devices for an enormous
range of electrical technologies -- radio,
microwave, radar, optical communications, lasers,
power generation and transmission, electronic
components, and others -- must be based on the
proper
understanding
and
application
of
Maxwell's equations.
The application of Maxwell's theory is at the
heart of some of the most exciting new
technologies -- lasers, fiber-optics, induction
motors, and the like. There is little question that
the future holds still more marvels stemming
from the use of Maxwell's wonderful equations.
Sir J.J. Thomson, 1931
Radio
Radio and the application of other parts of the
electromagnetic spectrum are the most obvious
technological products of the work of Maxwell.
Before the statement of his theory and his
equations, few people even suspected the
existence of electromagnetic waves. More than
25 years elapsed between the time Maxwell
predicted such waves and Hertz actually
produced and detected them. It did not take long
after that, however, for men like Oliver Lodge,
Guglielmo Marconi, and Aleksandr Popov to begin
transforming radio into a practical means of
communication. In 1896, Marconi and Popov both
sent radio messages over short distances, and
five years later Marconi transmitted the first
radio message across the Atlantic. In 1912, the
extraordinary growth of the new technology was
marked by the formation, in New York, of the
Institute of Radio Engineers (IRE). Fifty years
later, the IRE would become part of the Institute
of Electrical and Electronics Engineers.
G.C. Southworth with waveguide, Bell Laboratories
Radio towers, about 1912.
National Museum of American History,
Smithsonian Institution